Apparatus and method of manufacturing radiation detection panel

ABSTRACT

According to one embodiment, an apparatus of manufacturing a radiation detection panel, includes an evaporation source configured to evaporate a scintillator material and emit the scintillator material vertically upward, a holding mechanism located vertically above the evaporation source, and holding a photoelectric conversion substrate, and a heat conductor arranged opposite to the holding mechanism with a gap.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.14/301,460 filed Jun. 11, 2014, which is a Continuation Application ofPCT Application No. PCT/JP2012/081674, filed Dec. 6, 2012 and based uponand claiming the benefit of priority from prior Japanese PatentApplications No. 2011-276157, filed Dec. 16, 2011; No. 2011-276158,filed Dec. 16, 2011; No. 2011-276207, filed Dec. 16, 2011; and No.2011-276208, filed Dec. 16, 2011, the entire contents of all of whichare incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an apparatus and methodof manufacturing a radiation detection panel.

BACKGROUND

As radiation detection panels, X-ray detection panels have recently beenput to practical use. The X-ray detection panels include a fluorescentfilm for converting an X-ray (radioactive ray) into light, and aphotoelectric conversion element for converting the light into anelectric signal. Such X-ray detection panels can contribute to reductionof the size of the entire X-ray flat detector, compared to conventionalX-ray image tubes. The X-ray flat detector converts, into digitalelectric information, the image information corresponding to the X-rayshaving passed through an inspection target. The X-ray flat detector canprovide various digital information processing functions, such asdigital image processing and digital image storage.

The X-ray flat detector is widely used for various purposes, such asmedical and dental treatments of patients, industrial inspectionsincluding nondestructive inspections, scientific researches includingarchitectural analysis. In these fields, high-precision image extractionand high-speed image detection are possible by digital informationprocessing, with the result that the amount of undesirable X-ray(radioactive ray) exposure can be reduced, and prompt inspection, promptdiagnosis, etc., can be realized.

Scintillator material techniques are often diverted to the forming of afluorescent film for the X-ray flat detector. In the X-ray flatdetector, a scintillator material is formed of a material containing, asmain components, cesium (Cs) and iodine (I) used in the conventionalX-ray image tubes. The scintillator material, which contains cesiumiodide (CsI) as a main component and is to be grown into columnarcrystals, can enhance sensitivity and resolution by virtue of opticalguide effect, compared to another scintillator material forming granularcrystals.

To secure the X-ray flat detector in a highly sensitive state, it isnecessary to acquire light (fluorescent light) of a sufficientintensity, into which an X ray is converted, and to form the fluorescentfilm to a certain thickness. When a scintillator material containing CsIas a main component is used, the fluorescent film may often be formed toa thickness of about 500 μm.

On the other hand, the fluorescent film has a tendency to reduce theresolution of an image when its thickness is increased. In order for thefluorescent film to simultaneously have high sensitivity and highresolution, it is desirable to employ a deposition method capable offorming thinner columnar crystals of the scintillator material andforming the columnar crystals more uniformly in the thickness direction.

The conventional X-ray image tube manufacturing method and theconventional X-ray flat detector manufacturing method disclose filmforming methods associated with scintillator materials. Further, as asimilar manufacturing method, a method of manufacturing a radiationimage conversion panel using photostimulable phosphor is well known.

A manufacturing apparatus for depositing evaporated scintillatormaterial particles on the surface of a photoelectric conversionsubstrate comprises a vacuum chamber and a crucible placed in the vacuumchamber. When depositing the scintillator material, the photoelectricconversion substrate is arranged horizontally above the crucible in thevacuum chamber. After that, the scintillator material is heated in thecrucible and evaporated therefrom. As a result, the evaporatedscintillator material is deposited on the surface of the photoelectricconversion substrate. There is a case where the evaporated scintillatormaterial is deposited on the surface of the photoelectric conversionsubstrate, with the photoelectric conversion substrate kept rotated on ahorizontal plane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an X-ray flat detectorthat includes an X-ray detection panel produced by an X-ray detectionpanel manufacturing method according to an embodiment;

FIG. 2 is an exploded perspective view showing part of the X-ray flatdetector;

FIG. 3 schematically shows the structure of a vacuum deposition deviceaccording to the embodiment;

FIG. 4 is a graph showing changes in MTF relative value to therotational speed of a photoelectric conversion substrate;

FIG. 5 is a schematic view showing part of the vacuum deposition device,a crucible and the photoelectric conversion substrate;

FIG. 6 is another schematic view showing part of the vacuum depositiondevice, a crucible and the photoelectric conversion substrate;

FIG. 7 is a graph showing changes in a component ratio (Dh/Dv) relativeto a ratio (L/R), assumed when an incident angle θ₁ is set to 40°, 45°,50°, 60°, 70° and 75°;

FIG. 8 is a view showing a coordinate system in which the vacuumchamber, the crucible and the photoelectric conversion substrate shownin FIGS. 3 and 5 are made to correspond to coordinates;

FIG. 9 shows the coordinate system of FIG. 8 and the growing directionalcomponent of a columnar crystal at a point P at each moment;

FIG. 10 is a graph showing changes in the length of the perpendicularcomponent of a crystal growth vector relative to the length (=movingradius) from the center of a substrate, assumed under a predeterminedcondition when the incident angle is set to 45°, 50°, 55°, 60°, 65°, 70°and 75°;

FIG. 11 is a graph showing changes in the length of the component (alongthe moving radius) of the crystal growth vector relative to the length(=moving radius) from the center of the substrate, assumed under thepredetermined condition when the incident angle is set to 45°, 50°, 55°,60°, 65°, 70° and 75°;

FIG. 12 is a graph showing changes in the length of the perpendicularcomponent of the crystal growth vector relative to the length (=movingradius) from the center of the substrate, assumed under anotherpredetermined condition when the incident angle is set to 45°, 50°, 55°,60°, 65°, 70° and 75°;

FIG. 13 is a graph showing changes in the length of the component (alongthe moving radius) of the crystal growth vector relative to the length(=moving radius) from the center of the substrate, assumed under saidanother predetermined condition when the incident angle is set to 45°,50°, 55°, 60°, 65°, 70° and 75°; and

FIG. 14 shows the photoelectric conversion substrate, the heatconductor, the holding mechanism and radiator shown in FIG. 3, and is aschematic view for explaining the function of a heat conductor.

DETAILED DESCRIPTION

In general, according to one embodiment, there is provided an apparatusof manufacturing a radiation detection panel, comprising an evaporationsource configured to evaporate a scintillator material and emit thescintillator material vertically upward, a holding mechanism locatedvertically above the evaporation source, and holding a photoelectricconversion substrate such that a deposition surface of the photoelectricconversion substrate exposed to the evaporation source and inclined withrespect to a vertical axis, and a heat conductor positioned through theholding mechanism and away from the photoelectric conversion substrateand arranged opposite to the holding mechanism with a gap.

According to another embodiment, there is provided a method ofmanufacturing a radiation detection panel, comprising positioning aphotoelectric conversion substrate vertically above an evaporationsource such that a deposition surface of the photoelectric conversionsubstrate is exposed to the evaporation source and inclined with respectto a vertical axis, evaporating a scintillator material and emitting thescintillator material vertically upward by the evaporation source todeposit a fluorescent film on the deposition surface, and controlling atemperature of the photoelectric conversion substrate within a range of70° to 140° in an initial deposition stage, and controlling thetemperature of the photoelectric conversion substrate within a range of125° to 190° after the initial deposition stage.

Referring now to the accompanying drawings, a detailed description willbe given of a method and apparatus of manufacturing an X-ray detectionpanel according to an embodiment. Firstly, the structure of the X-raydetection panel manufactured by the X-ray detection panel manufacturingmethod will be described. The overall structure of the X-ray flatdetector using the X-ray detection panel will also be described.

FIG. 1 is a schematic cross-sectional view of the X-ray flat detector.As shown in FIG. 1, the X-ray flat detector is of a large size. TheX-ray flat detector comprises an X-ray detection panel 2, amoisture-proof cover 3, a supporting substrate 4, a circuit board 5, anX-ray shielding lead plate 6, a heat-dissipating insulating sheet 7, aconnection member 8, a housing 9, a flexible printed circuit 10 and anincident window 11.

FIG. 2 is an exploded perspective view showing part of the X-ray flatdetector. As shown in FIGS. 1 and 2, the X-ray detection panel 2includes a photoelectric conversion substrate 21 and a fluorescent film22. The photoelectric conversion substrate 21 includes a glass substratewith a thickness of 0.7 mm, and a plurality of photodetectors 28two-dimensionally arranged on the glass substrate. The photodetectors 28each include a thin film transistor (TFT) 26 as a switching element, anda photodiode (PD) 27 as a photosensor. The TFT 26 and PD 27 are formedusing, for example, amorphous silicon (a-Si) as a matrix. Thephotoelectric conversion substrate 21 has, for example, a square shapewith one side of 50 cm. In large X-ray flat detectors, the photoelectricconversion substrate 21 has one side of, for example, 13 to 17 inches.

The fluorescent film 22 is arranged directly on the photoelectricconversion substrate 21. The fluorescent film 22 is positioned on theX-ray incident side of the photoelectric conversion substrate 21. Thefluorescent film 22 is used to convert an X ray into light (fluorescentlight). The PD 27 is used to convert the light from the fluorescent film22 into an electric signal.

The fluorescent film 22 is formed by depositing a scintillator materialon the photoelectric conversion substrate 21. As the scintillatormaterial, a material containing cesium iodide (CsI) as a main componentcan be used. The thickness of the fluorescent film 22 is set within arange of 100 to 1000 μm. More preferably, the thickness of thefluorescent film 22 is set within a range of 200 to 600 μm in view ofsensitivity and resolution.

In the embodiment, the thickness of the fluorescent film 22 is adjustedto 500 μm. Further, as the scintillator material, a material obtainingby adding thallium (Tl) or thallium iodide (TlI) to cesium iodide (CsI)as the main component is used. As a result, the fluorescent film 22 canemit light (fluorescent light) of an appropriate wavelength uponreceiving an X ray.

For instance, it is preferable that the amount of added thallium iodide(TlI) be several % or less in concentration, and hence the amount ofcesium iodide (CsI) in the scintillator material be 95% or more inconcentration.

As shown in FIG. 1, the moisture-proof cover 3 completely covers thefluorescent film 22 to seal the same. The moisture-proof cover 3 isformed of, for example, an aluminum alloy. If the thickness of themoisture-proof cover 3 is increased, an X-ray dosage entering thefluorescent film 22 is decreased to thereby degrade the sensitivity ofthe X-ray detection panel 2. Therefore, it is desirable that themoisture-proof cover 3 should be formed as thin as possible. To set thethickness of the moisture-proof cover 3, consideration is given tobalance in various parameters (the stableness of the shape of themoisture-proof cover 3, the manufacturing tolerant strength of the same,the attenuation of the X-ray entering the fluorescent film 22). Thethickness of the moisture-proof cover 3 is set within a range of 50 to500 μm. In the embodiment, the thickness of the moisture-proof cover 3is adjusted to 200 μm.

A plurality of pads to be connected to the outside are provided on theouter periphery of the photoelectric conversion substrate 21. The padsare used for output of detecting signal and input of electric signal fordriving the photoelectric substrate 21.

Since the assembly of the X-ray detection panel 2 and the moisture-proofcover 3 is formed by stacking thin members, it is light and weak.Therefore, the X-ray detection panel 2 is secured to a flat surface ofthe supporting substrate 4 via an adhesive sheet. The supportingsubstrate 4 is formed of, for example, an aluminum alloy, and has astrength necessary to reliably support the X-ray detection panel 2.

The circuit board 5 is secured to the other surface of the supportingsubstrate 4 via the lead plate 6 and the heat-dissipating insulatingsheet 7. The circuit board 5 is fixed to the supporting substrate 4 bymeans of, for example, screws. The circuit board 5 and the X-raydetection panel 2 are connected to each other via the flexible printedcircuit 10. Thermal compression bond utilizing an anisotropic conductivefilm (ACF) is used for the connection of the flexible printed circuit 10and the photoelectric conversion substrate 21. By virtue of this method,electrical connection of a plurality of fine signal lines is secured. Aconnector corresponding to the flexible printed circuit 10 is mounted onthe circuit board 5. The circuit board 5 is electrically connected tothe X-ray detection panel 2 via the connector. The circuit board 5 isconfigured to electrically drive the X-ray detection panel 2 andelectrically process signals output from the X-ray detection panel 2.

The housing 9 houses the X-ray detection panel 2, the moisture-proofcover 3, the supporting substrate 4, the circuit board 5, the lead plate6, the heat-dissipating insulating sheet 7, and the connection member 8.The housing 9 has an opening formed in a position opposing the X-raydetection panel 2. The connection member 8 is secured to the housing 9to support the supporting substrate 4.

The incident window 11 is fitted in the opening of the housing 9 to sealthe opening. X-rays are permitted to pass through the incident window 11and reach the X-ray detection panel 2. The incident window 11 is formedflat and has a function of protecting the interior of the housing 9. Itis desirable to form the incident window 11 of a thin member having alow X-ray absorption factor. By virtue of this structure, the degree ofscattering of X rays and the attenuation of the X-ray dosage on theincident window 11 can be reduced, whereby a thin and light X-raydetector can be realized. The X-ray detector is constructed as describedbelow.

A description will be given of a vacuum deposition device used in anapparatus for manufacturing the X-ray detection panel 2.

FIG. 3 schematically shows the structure of a vacuum deposition device30. As shown in FIG. 3, the vacuum deposition device 30 includes avacuum chamber 31, a crucible 32 as a vapor source for thermally meltingand evaporating the scintillator material, heaters 33 and 34, a cover35, heat conductors 36, holding mechanisms 37, radiator 38 astemperature adjusting members, and motors 39.

The vacuum chamber 31 is formed in a rectangular shape with a greaterheight (vertical dimension) than a width (horizontal dimension). Avacuum exhaust device (vacuum pump) (not shown) is attached to thevacuum chamber 31. The vacuum exhaust device can hold the interior ofthe vacuum chamber 31 under the atmospheric pressure. The vacuumdeposition device 30 utilizes vacuum deposition method performed under adesired pressure below the atmospheric pressure.

The crucible 32 is located in a lower position in the vacuum chamber 31.A scintillator material obtained by adding TlI to CsI as the maincomponent is input into the crucible 32. For instance, a scintillatormaterial containing cesium iodide (CsI) with a concentration of 95% ormore can be used. There is another method of inputting a scintillatormaterial containing cesium iodide (CsI) with a concentration of 100%,and evaporating a small amount of thallium iodide (TlI) from anothersmall crucible. Even in the latter case, the structure of the columnarcrystal is determined by cesium iodide (CsI), and therefore the samedescription can be given of the advantage associated with thearrangement of the crucible 32 in the vacuum chamber 31.

The crucible 32 has a central upper end portion formed cylindrical (likea chimney pipe) and protruded in the height direction of the vacuumchamber 31. An evaporation port 32 a positioned at the tip of thecrucible 32 is upwardly open in the vacuum chamber 31. The scintillatormaterial is emitted vertically upward at the center the vertical axisthrough the center of the evaporation port 32 a.

A heater 33 is provided around the crucible 32. The heater 33 isconfigured to heat the crucible 32 so as to adjusted the temperature ofthe same to a value higher than the melting point of the scintillatormaterial. In the embodiment, the heater 33 heats the crucible 32 toabout 700° C. The temperature of the crucible 32 can be measured by athermometer (not shown), and the temperature monitoring of the crucible32 and the driving of the heater 33 can be performed by a heater drivingmechanism (not shown).

When the crucible 32 has been heated as described above, evaporatedelement particles of the scintillator material are upwardly emittedthrough the evaporation port 32 a of the crucible 32 in the vacuumchamber 31. Further, since the upper end portion of the crucible 32 isformed cylindrical, the scintillator material can be emitted with highdirectivity. By virtue of the above structure, the scintillator materialis intensively emitted in the direction in which the photoelectricconversion substrate(s) 21 is located. By adjusting the length of theupper end portion of the crucible 32, the directivity of the emission ofthe scintillator material can be adjusted.

In the embodiment, to produce a large X-ray detection panel 2, it isnecessary to deposit a great amount (e.g., 400 g) of scintillatormaterial on the photoelectric conversion substrate 21. To this end, alarge crucible 32 is employed and several kilograms (e.g., 6 kg) or moreof scintillator material is input in the crucible.

A heater 34 is provided around the tip portion of the crucible 32 toheat the tip portion. As a result, blocking of the tip portion of thecrucible 32 can be prevented.

The cover 35 covers the crucible 32 and the heaters 33 and 34 tosuppress unnecessary radiation of heat from them. The cooling channelthrough which coolant (for example, water) flows is formed in the cover35.

The heat conductors 36 are provided in upper positions in the vacuumchamber 31 and secured thereto. The heat conductors 36 are each in theshape of, for example, a plate with a thickness of 3 mm. The heatconductors 36 may be formed of, for example, aluminum. The heatconductors 36 have a function of transmitting the heat of the heatdissipating members 38 to the photoelectric conversion substrate 21 andthe holding mechanisms 37, and transmitting the heat of thephotoelectric conversion substrate 21 and the holding mechanisms 37 tothe radiators 38. The heat conductors 36 also have a function ofpreventing the scintillator material from adhering to, for example, theradiators 38.

The holding mechanisms 37 are arranged in positions that oppose therespective heat conductors 36 and are closer than the heat conductors 36to the center of the vacuum chamber 31. The holding mechanisms 37 holdthe photoelectric conversion substrates 21, with the film-depositedsurfaces of the photoelectric conversion substrates 21 exposed. Further,the holding mechanisms 37 hold the photoelectric conversion substrates21 with the film-deposited surfaces inclined to form an acute angle withrespect to the height direction of the vacuum chamber 31.

The radiators 38 are arranged in positions that oppose the respectiveheat conductors 36 and are closer than the heat conductors 36 to therespective side walls of the vacuum chamber 31. The radiators 38 areconnected to the vacuum chamber 31 to transmit the heat occurring in theradiators 38 to the chamber 31. Each of the radiators 38 is an assemblyof a heat conductor and a heater, although not shown in detail. Theheater of each radiator 38 is used to heat the correspondingphotoelectric conversion substrate 21. The temperature of eachphotoelectric conversion substrate 21 can be measured by a thermometer(not shown), and the temperature monitoring of each photoelectricconversion substrate 21 and the driving of the heater of each radiator38 can be performed by a heater driving mechanism (not shown).

The heat generated by the heater of the radiator 38 is transmitted tothe photoelectric conversion substrate 21 via the heat conductor 36 bythe heat conduction. The heat generated by the heater of the radiator 38may be transmitted to the photoelectric conversion substrate 21 via theheat conductor of the radiator 38 and the holding mechanism 37.

On the other hand, the heat of the photoelectric conversion substrate 21is transmitted to the heat conductor of the radiator 38 via the heatconductor 36 by the heat conduction. The heat of the photoelectricconversion substrate 21 may be transmitted to the radiator 38 via theholding mechanism 37. The heat transmitted to the heat conductor of theradiator 38 is then transmitted to the vacuum chamber 31.

The motors 39 are airtightly attached to the vacuum chamber 31. Theshaft of each motor 39 extends through the through holes formed in thecorresponding radiator 38 and heat conductor 36. The holding mechanisms37 are detachably attached to the respective shafts of the motors 39.The respective centers of the photoelectric conversion substrates 21oppose the shafts of the motors 39. When the motors 39 operate, theholding mechanisms 37 rotate, with the result that the photoelectricconversion substrates 21 rotate about their respective rotation axesextending along the respective normal lines of the centers of thephotoelectric conversion substrates 21.

In the embodiment, the vacuum deposition device 30 incorporates two heatconductors 36, two holding mechanisms 37, two radiators 38 and twomotors 39. Accordingly, the vacuum deposition device 30 cansimultaneously form two fluorescent films 22 on the two photoelectricconversion substrates 21. The two holding mechanisms 37 are arranged insymmetrical positions with respect to the vertical axis passing throughthe evaporation port 32 a. Further, the two holding mechanisms 37 areobliquely arranged so as to make the respective film-deposited surfacesof the photoelectric conversion substrates 21 face each other. The angleα accomplished inside the respective film-deposited surfaces of thephotoelectric conversion substrates 21 is an acute angle. The vacuumdeposition device 30 is constructed as described above.

The evaporated element particles of the scintillator material emittedthrough the evaporation port of the crucible 32 are deposited on thephotoelectric conversion substrates 21 provided in upper positions inthe vacuum chamber 31. At this time, the evaporated element particles ofthe scintillator material are obliquely emitted onto the photoelectricconversion substrates 21. The angle of incidence of the scintillatormaterial particles on each photoelectric conversion substrate 21 is setas θ. The incident angle θ is an angle made inside between the normalline of each photoelectric conversion substrate 21 and the line of theincident direction of the scintillator material (i.e., the imaginaryline connecting the center of the evaporation port 32 a to an arbitrarypoint on the film-deposited surface of each substrate 21).

In the embodiment, θ=60° at the central portion of each photoelectricconversion substrate 21, θ=70° at the uppermost portion of eachphotoelectric conversion substrate 21 (i.e., the end portion of eachphotoelectric conversion substrate 21 close to the ceiling wall of thevacuum chamber 31), and θ=45° at the lowermost portion of eachphotoelectric conversion substrate 21 (i.e., the end portion of eachphotoelectric conversion substrate 21 close to the crucible 32).

Compared to a vacuum deposition device where θ=0°, the vacuum depositiondevice 30 constructed as the above can reduce the required volume of thevacuum chamber 31. As a result, the load on, for example, the vacuumexhaust device can be reduced. Further, the time required for vacuumingcan be shortened, the productivity can be enhanced.

Furthermore, in the vacuum deposition device 30, the efficiency of useof the scintillator material can be significantly enhanced.

A description will now be given of a method of manufacturing thefluorescent film 22 using the vacuum deposition device 30, included in amethod of manufacturing the X-ray detection panel 2.

At the start of the manufacture of the fluorescent film 22, the vacuumdeposition device 30 and the photoelectric conversion substrates 21including photodetectors 28 are prepared. Subsequently, thephotoelectric conversion substrates 21 are attached to the respectiveholding mechanisms 37. After that, the holding mechanisms 37 with thephotoelectric conversion substrates 21 are carried into the vacuumchamber 31 and attached to the respective shafts of the motors 39.

Thereafter, the vacuum chamber 31 is airtightly closed, and is vacuumedusing a vacuum exhaust device. Subsequently, the motors 39 are operatedto rotate the photoelectric conversion substrates 21. The timing of theoperation of the motors 39 is not limited, but may be changed in variousways. For instance, the timing of start operation of the motors 39 maybe adjusted based on the monitored temperature of the crucible 32.

After that, the heating of the crucible 32 using the heaters 33 and 34,and the circulation of a coolant in a coolant path formed in the cover35 are started. At this time, the scintillator material in the crucible32 is evaporated and deposited on the photoelectric conversionsubstrates 21. Since the scintillator material deposited on thephotoelectric conversion substrates 21 has heat, it heats thephotoelectric conversion substrates 21 during the deposition period. Bythus depositing the scintillator material on the photoelectricconversion substrates 21, fluorescent films 22 (see FIG. 2) are formedon the photoelectric conversion substrates 21. This is the terminationof the manufacture of the fluorescent films 22.

A description will then be given of the pressure in the vacuum chamber31.

The element particles of the scintillator material evaporated anddeposited on the photoelectric conversion substrates 21 form crystalthereon. In the initial stage of deposition, fine crystal grains areformed on the photoelectric conversion substrates 21. However, when thedeposition is continued, the crystal grains will grow into a columnarcrystal. The growth direction of the columnar crystal is opposite to theincident direction of the evaporated element particles. Therefore, whenthe evaporated element particles are obliquely deposited on thephotoelectric conversion substrates 21, oblique growth of the columnarcrystal occurs on the substrates 21.

To suppress such oblique growth of the columnar crystal and put aheadcolumnar crystal growth along the normal lines of the photoelectricconversion substrates 21, in the conventional methods, an inactive gas,such as argon (Ar), is introduced into the vacuum chamber 31 duringdeposition, thereby increasing the pressure in the vacuum chamber 31 toabout 1×10⁻² to 1 Pa. By virtue of the introduced inactive gas, theevaporated element particles are flown and guided onto the photoelectricconversion substrates 21 from many directions. As a result, the growthdirection of the columnar crystal becomes parallel to the normal line ofeach photoelectric conversion substrate 21.

However, when the pressure in the vacuum chamber 31 is increased by theintroduction of the inactive gas, the evaporated element particles areguided onto the photoelectric conversion substrates 21 from alldirections, and hence the columnar crystal growth is accelerated also ina direction in which the columnar crystal is thickened. As a result, athick columnar crystal is formed, which degrades the resolution of theX-ray detection panel 2. To overcome this problem, in the embodiment,when the scintillator material is deposited on the photoelectricconversion substrates 21, no inactive gas is introduced. Instead, vacuumdeposition performed with a vacuum pressure of 1×10⁻² Pa or lessmaintained is utilized. This can suppress columnar crystal thickeninggrowth, and accelerate crystal growth in direction along the normal lineof each photoelectric conversion substrate 21.

The rotational speed of the photoelectric conversion substrates 21 willbe described.

To average the incident directions of the evaporated element particleson the photoelectric conversion substrates 21, the photoelectricconversion substrates 21 are rotated when the scintillator material isdeposited thereon. This enables the thickness of the fluorescent films22 to be uniform over the entire surface of each photoelectricconversion substrate 21.

Further, the directions of the crystal growth vectors can be averaged,whereby the columnar crystal can be grown in direction along the normalline of each photoelectric conversion substrate 21 as a whole. Thedirection of the crystal growth vector corresponds to the growthdirection of the columnar crystal. As a result, a thinner columnarcrystal can be formed to thereby enhance the resolution of the X-raydetection panel 2.

To average the directions of the above-mentioned crystal growth vectors,the rotational speed of the photoelectric conversion substrates 21 is anessential factor. The inventors of the present application measuredmodulation transfer function (MTF) values relative to the rotationalspeed of each photoelectric conversion substrate 21. Results of anexamination are shown in FIG. 4. FIG. 4 is a graph showing changes inMTF relative value to the rotational speed of a photoelectric conversionsubstrate 21. FIG. 4 shows MTF values associated with the peripheralportion of each photoelectric conversion substrate 21, obtained when therotational speed of each photoelectric conversion substrate 21 is set to2 rpm, 4 rpm and 6 rpm, and MTF values associated with the centralportion of each photoelectric conversion substrate 21, obtained when therotational speed of each photoelectric conversion substrate 21 is set to2 rpm, 6 rpm and 10 rpm.

FIG. 4 does not show MTF values associated with the peripheral portionof each photoelectric conversion substrate 21, obtained when therotational speed of each photoelectric conversion substrate 21 is set to10 rpm, and MTF values associated with the central portion of eachphotoelectric conversion substrate 21, obtained when the rotationalspeed of each photoelectric conversion substrate 21 is set to 4 rpm.However, it can be understood that when the rotational speed of eachphotoelectric conversion substrate 21 is changed, the MTF valuesassociated with the central portion of each photoelectric conversionsubstrate 21 and peripheral portions of each photoelectric conversionsubstrate 21 change substantially similarly. It is also understood thatwhen the rotational speed of each photoelectric conversion substrate 21becomes less than 4 rpm, the MTF values significantly drop.

In contrast, it can be understood that when the rotational speed of eachphotoelectric conversion substrate 21 becomes 4 rpm or more, the MTFvalues gradually increase. Therefore, when the photoelectric conversionsubstrates 21 are rotated, it is desirable that the rotational speed ofthe photoelectric conversion substrates 21 be set to 4 rpm or more. Itis further desirable that the rotational speed of each photoelectricconversion substrate 21 be kept constant during deposition.

A description will be given of a lower limit for the incident angle θ atthe center of each photoelectric conversion substrate 21.

Although in the embodiment, the vacuum deposition device 30 is formed toset θ=60° at the center of each photoelectric conversion substrate 21,the device is not limited to this but can be modified in various ways.The vacuum deposition device 30 may be formed to set θ<60° at the centerof each photoelectric conversion substrate 21. However, the closer to 0°the incident angle θ, the greater the portion of the deposition surfaceof each photoelectric conversion substrate 21 that faces the bottom wallof the vacuum chamber 31. Namely, when the incident angle θ is closer to0°, the width of the vacuum chamber 31 is greater, and hence the volumeof the vacuum chamber 31 is greater. This is conspicuous when thephotoelectric conversion substrates 21 are large.

Further, the volume compression rate of the vacuum chamber 31 issubstantially proportional to sin θ (sine of the incident angle θ). Inother words, the volume of the vacuum chamber 31 is substantiallyproportional to cos θ. Accordingly, when 0°≤θ<45°, the volumecompression rate of the vacuum chamber 31 is relatively low, while whenθ=45°, at last the volume compression rate of the vacuum chamber 31 isapprox. 70%. Further, when 45°<θ, the volume compression rate is moregreatly changes than in the case of θ=45°, whereby the volumecompression rate of the vacuum chamber 31 is further increased. As aresult, a more efficient reduction effect in the volume of the vacuumchamber 31 can be realized.

Consequently, when the apparatus load and productivity of, for example,the vacuum exhaust device, and the efficient use of the scintillatormaterial are considered, it is desirable to form the vacuum depositiondevice 30 so that 45°≤θ is set at the center of each photoelectricconversion substrate 21.

A description will now be given of an upper limit for the incident angleθ at the center of each photoelectric conversion substrate 21.

FIG. 5 is a schematic view of part of the vacuum deposition device 30,showing the crucible 32 and one of the photoelectric conversionsubstrates 21. As shown in FIG. 5, the incident angle θ at the center ofthe deposition surface of the photoelectric conversion substrate 21 isset as θ₁. Further, the distance (linear distance) from the evaporationport 32 a of the crucible 32 to the center of (the deposition surfaceof) the photoelectric conversion substrates 21 is R, and the length ofthe photoelectric conversion substrate 21 from designated position tothe center thereof along the surface thereof is L.

In a complete vacuum state, crystal grows in the direction opposite tothe incident direction of evaporated element particles. Since thephotoelectric conversion substrate 21 is rotated during the deposition,the growth directions of the columnar crystals at respective portions ofthe photoelectric conversion substrate 21 are determined from theintegration results of deposition vectors Va (Va1, Va2, Va3). Thedirections of the deposition vectors are the incident directions of theevaporated element particles.

FIG. 6 is another schematic view of part of the vacuum deposition device30, showing the crucible 32 and one of the photoelectric conversionsubstrates 21. It can be understood from FIG. 6 that at the uppermostportion of the photoelectric conversion substrate 21, the crystal growthvector is directed inwardly with respect to the photoelectric conversionsubstrate 21 (see, for example, a crystal growth vector Vb2). Incontrast, it can be understood that at the lowermost portion of thephotoelectric conversion substrate 21, the crystal growth vector isdirected outwardly with respect to the photoelectric conversionsubstrate 21 (see, for example, a crystal growth vector Vb1). Since thephotoelectric conversion substrate 21 is rotated during the deposition,the components of the crystal growth vectors Vb (Vb1, Vb2) that areparallel to the surface of the photoelectric conversion substrate 21 areoffset.

Assume here that the component of each crystal growth vector Vb alongthe surface of the photoelectric conversion substrate 21 is Dh, and thatthe component of each crystal growth vector Vb along the normal line ofthe photoelectric conversion substrate 21 is Dv. Assuming as a simplesimulation that the magnitude of each crystal growth vector Vb isinversely proportional to the square of the distance R, the componentsDh and Dv at a position of the length L from the center of thephotoelectric conversion substrate 21 are given by the followingequations:

$\begin{matrix}{\mspace{79mu}\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack} & \; \\{D_{h} = {\frac{1}{R^{2}}\left\{ {\frac{{\sin\;\theta_{1}} + x}{\left( {1 + x^{2} + {2{x \cdot \sin}\;\theta_{1}}} \right)^{3/2}} + \frac{{\sin\;\theta_{1}} - x}{\left( {1 + x^{2} - {2{x \cdot \sin}\;\theta_{1}}} \right)^{3/2}}} \right\}}} & {{Formula}\mspace{14mu} 1} \\{\mspace{79mu}\left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack} & \; \\{D_{v} = {\frac{1}{R^{2}}\left\{ {\frac{1}{\left( {1 + x^{2} + {2{x \cdot \sin}\;\theta_{1}}} \right)^{3/2}} + \frac{1}{\left( {1 + x^{2} - {2{x \cdot \sin}\;\theta_{1}}} \right)^{3/2}}} \right\} \times \cos\;\theta_{1}}} & {{Formula}\mspace{14mu} 2}\end{matrix}$

The influence degree of the columnar crystal growth in the directionalong the surface of the photoelectric conversion substrate 21 can beestimated by the component ratio (Dh/Dv) of the components Dh and Dv. Inthe above equations, x is the value that characterizes the relativedistance between the photoelectric conversion substrate 21 and theevaporation port 32 a of the crucible 32, and is the ratio (L/R) betweenthe length L and the distance R (i.e., x=L/R).

FIG. 7 is a graph showing changes in the crystal growth vector componentratio (Dh/Dv) relative to the ratio (L/R) between the length L and thedistance R, assumed when the incident angle θ₁ is set to 40°, 45°, 50°,60°, 70° and 75°. In the vertical axis of FIG. 7, “+” indicates theinward direction of the photoelectric conversion substrate 21, and “−”indicates the outward direction of the photoelectric conversionsubstrate 21. FIG. 7 shows simulation results obtained using the aboveformulas 1 and 2. As shown in FIG. 7, when the one side of thephotoelectric conversion substrate 21 is 50 cm, the length L fallswithin a range of 0 to 25 cm. The distance R is actually a value in thevicinity of 150 cm (i.e., a value of from 100 cm and several tensmillimeters to 200 cm) from the structure of the vacuum depositiondevice 30. Accordingly, the ratio (L/R) falls within a range of 0.15 to0.2. In view of this range, it can be understood that if the incidentangle θ₁ is 70° or less, the ratio (Dh/Dv) can be set to less than 1.

In the actual growth of the columnar crystal, the component ratio(Dh/Dv) becomes lower than the values shown in FIG. 7 (becomes closer to0) since forward deviation of the evaporation amount called a cosinerule occurs or there is an influence of a small amount of residual gas.

In view of the above-mentioned upper and lower limits for the incidentangle θ, it is appropriate if 45°≤θ₁≤70°. The above is a descriptionconcerning a simple simulation result.

The inventors made finer and more accurate simulations of the rotationeffect of the photoelectric conversion substrate 21. As a result, it wasdetected that if 50°≤θ₁≤65″, a good crystal perpendicular property (agood acceleration property of crystal growth in direction along thenormal line of the photoelectric conversion substrate 21) can beobtained. It was detected that if 55°≤θ₁≤60°, a better crystalperpendicular property can be obtained, i.e., the inclination of thecolumnar crystal becomes substantially zero.

The content of the above fine and accurate simulation will be described.

To create model formulas concerning oblique deposition, it is importantwhat type of coordinate system is employed. In light of the rotation ofthe photoelectric conversion substrate 21, such a coordinate system asshown in FIG. 8 is set. FIG. 8 shows a coordinate system in whichcoordinates are made to correspond to the vacuum chamber 31, thecrucible 32 and the photoelectric conversion substrate 21.

As shown in FIG. 8, the deposition surface of the photoelectricconversion substrate 21 is set as the X-Y plane, and the rotation axis(the axis along the normal line of the center of the deposition surface)of the photoelectric conversion substrate 21 is set as the Z axis. Apoint O corresponds to the center of the evaporation port 32 a. Thecentral axis (vertical axis) of the crucible 32 passing through thepoint O is positioned on the X-Y plane. The intersection of the centralaxis of the crucible 32 and the X axis is set as T. For instance, thepoint T corresponds to the vertex of the vacuum deposition device 30. Itcan be assumed that evaporated element particles of the scintillatormaterial are emitted from the point O in all directions symmetricallywith respect to the central axis of the crucible 32.

The incident angle θ₁ is a parameter characterizing oblique deposition,and is the angle made inside between the line segment connecting theorigin of the coordinate system and the point O, and the Z axis. A pointP exists on the deposition surface (X-Y plane) of the photoelectricconversion substrate 21, and expresses the position of deposition.Assuming that the moving radius (the linear distance between thecoordinate origin and the point p) is L, and the rotation angle is ϕ,the X coordinate Xp, the Y coordinate Xp and the Z coordinate Zp of thepoint P can be expressed as follows:Xp=L×cos ϕYp=L×sin ϕZp=0

Further, the moving radius L is not longer than the linear distance LObetween the coordinate origin and the point P. Namely, L≤L_(O), and morepractically, L<L_(O). Furthermore, the angle made inside between thecentral axis (segment CT) of the crucible 32 and the line (segment OP)of incidence at the point P is η.

Firstly, a general formula will be derived. When deriving the generalformula, the following four points are assumed:

(1) The interior of the vacuum chamber 31 is set in a sufficiently highvacuum state, and the evaporated element particles emitted from thecrucible 32 directly reach the deposition surface of the photoelectricconversion substrate 21.

(2) The evaporated element particles are emitted symmetrically (axialsymmetry) with respect to the central axis of the crucible 32.

(3) The direction of growth of columnar crystal at each instance isopposite to the incident direction of the evaporated element particles.

(4) The photoelectric conversion substrate 21 is rotated uniformly.Namely, the angle ϕ varies uniformly.

To derive the general formula, based on the coordinate system, thecoordinates of the point P are expressed by the following formula 3, thecoordinates of the point O are expressed by the following formula 4, thecoordinates of the point T are expressed by the following formula 5, thevector from the point O to the point T is expressed by the followingformula 6, and the vector from the point O to the point P is expressedby the following formula 7:

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack & \; \\{P = \begin{pmatrix}{L\;\cos\;\phi} \\{L\;\sin\;\phi} \\0\end{pmatrix}} & {{Formula}\mspace{14mu} 3} \\\left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack & \; \\{O = \begin{pmatrix}{R\;\sin\;\theta_{1}} \\0 \\{R\;\cos\;\theta_{1}}\end{pmatrix}} & {{Formula}\mspace{14mu} 4} \\\left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack & \; \\{T = \begin{pmatrix}{- L_{O}} \\0 \\0\end{pmatrix}} & {{Formula}\mspace{14mu} 5} \\\left\lbrack {{Formula}\mspace{14mu} 6} \right\rbrack & \; \\{{\overset{\rightharpoonup}{T} \equiv \overset{\rightharpoonup}{OT}} = \begin{pmatrix}{{- L_{O}} - {R\;\sin\;\theta_{1}}} \\0 \\{{- R}\;\cos\;\theta_{1}}\end{pmatrix}} & {{Formula}\mspace{14mu} 6} \\\left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack & \; \\{{\overset{\rightharpoonup}{W} \equiv \overset{\rightharpoonup}{OP}} = \begin{pmatrix}{{L\;\cos\;\phi} - {R\;\sin\;\theta_{1}}} \\{L\;\sin\;\phi} \\{{- R}\;\cos\;\theta_{1}}\end{pmatrix}} & {{Formula}\mspace{14mu} 7}\end{matrix}$

Further, the following formula 8 is derived from the formula 6, and thefollowing formula 9 is derived from the formula 7:[Formula 8]| T| ² =L _(O) ² +R ²+2L _(O) R sin θ  Formula 8[Formula 9]| W| ² =L ² +R ²−2LR sin θ₁ cos ϕ  Formula 9

FIG. 9 shows a coordinate system corresponding to the coordinate systemof FIG. 8, and shows the growth direction (crystal growth vector)component of the columnar crystal at each instance (point P). As shownin FIG. 9, it is assumed that the component perpendicular to the(deposition surface of the) photoelectric conversion substrate 21 is Da,the component along the moving radius is Db, and the component in therotation direction (ϕ direction) is Dc. Attention has been paid to therelative values of the components, and the coefficients for thecomponents are all set to 1. The components Da, Db and Dc are given bythe following Formulas 10, 11 and 12, respectively:

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 10} \right\rbrack & \; \\{D_{a} = {\frac{1}{{\overset{\rightharpoonup}{W}}^{2}} \times {f(\eta)} \times \frac{R\;\cos\;\theta_{1}}{\overset{\rightharpoonup}{W}}}} & {{Formula}\mspace{14mu} 10} \\\left\lbrack {{Formula}\mspace{14mu} 11} \right\rbrack & \; \\{D_{b} = {\frac{1}{{\overset{\rightharpoonup}{W}}^{2}} \times {f(\eta)} \times \frac{{R\;\sin\;\theta_{1}\cos\;\phi} - L}{\overset{\rightharpoonup}{W}}}} & {{Formula}\mspace{14mu} 11} \\\left\lbrack {{Formula}\mspace{14mu} 12} \right\rbrack & \; \\{D_{c} = {\frac{1}{{\overset{\rightharpoonup}{W}}^{2}} \times {f(\eta)} \times \frac{\left( {{- R}\;\sin\;\theta_{1}\sin\;\phi} \right)}{\overset{\rightharpoonup}{W}}}} & {{Formula}\mspace{14mu} 12}\end{matrix}$

f(η) is a function expressing a distribution of evaporated elementparticles, and is a function of η in view of axis symmetry. Further, ηitself is a function depending upon θ₁, ϕ, L, L_(O) and R, i.e., η (θ₁,ϕ, L, L_(O), R).

Based on the above, the growth directional component of the columnarcrystal at the point P, which is obtained over the long term, can beobtained. Further, it should be noted that η and f are even functionsassociated with ϕ, as is evident from FIG. 8. In order to consider theeffect of the rotation of the photoelectric conversion substrate 21, itis sufficient if integration is performed in association with ϕ.

The component perpendicular to (the deposition surface of) thephotoelectric conversion substrate 21 is given by the following formula13, and the moving direction component is given by the following formula14:

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 13} \right\rbrack & \; \\{\int_{- \pi}^{\pi}\ {d\;\phi\frac{1}{{\overset{\rightharpoonup}{W}}^{2}} \times {f(\eta)} \times \frac{R\;\cos\;\theta_{1}}{\overset{\rightharpoonup}{W}}}} & {{Formula}\mspace{14mu} 13} \\\left\lbrack {{Formula}\mspace{14mu} 14} \right\rbrack & \; \\{\int_{- \pi}^{\pi}\ {d\;\phi\frac{1}{{\overset{\rightharpoonup}{W}}^{2}} \times {f(\eta)} \times \frac{{R\;\sin\;\theta_{1}\cos\;\phi} - L}{\overset{\rightharpoonup}{W}}}} & {{Formula}\mspace{14mu} 14}\end{matrix}$

Further, the component in the rotation direction (ϕ direction) becomeszero (0) since it is obtained by integration of an odd functionassociated with ϕ.

To perform more specific calculation, a specific function form of f(η)is needed. As mentioned above, the angle distribution of evaporationfrom a minute plane can be approximated by the cosine rule. Accordingly,an approximation model of f(η)=cos (η) is employed. More specifically,the following relational formulas 15 and 16 are utilized:

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 15} \right\rbrack & \; \\{{\cos\;\eta} = \frac{\left( {\overset{\rightharpoonup}{T},\overset{\rightharpoonup}{W}} \right)}{{\overset{\rightharpoonup}{T}}{\overset{\rightharpoonup}{W}}}} & {{Formula}\mspace{14mu} 15} \\\left\lbrack {{Formula}\mspace{14mu} 16} \right\rbrack & \; \\{\left( {\overset{\rightharpoonup}{T},\overset{\rightharpoonup}{W}} \right) = {R^{2} + {L_{O}R\;\sin\;\theta} - {\left( {{LL}_{O} + {{LR}\;\sin\;\theta_{1}}} \right)\;\cos\;\phi}}} & {{Formula}\mspace{14mu} 16}\end{matrix}$

It should be noted that T is a function that does not contain ϕ. In viewof the above, a deposition model formula utilizing the rule of cosinecan be obtained. The following formulas 17, 18 and 19 express adeposition model formula utilizing the rule of cosine. The formula 17expresses a component perpendicular to (the deposition surface of) thephotoelectric conversion substrate 21, the formula 18 expresses acomponent in the moving radius direction, and the formula 19 expresses acomponent in the rotation direction (ϕ direction).

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 17} \right\rbrack & \; \\{\int_{- \pi}^{\pi}\ {d\;\phi\frac{\left( {\overset{\rightharpoonup}{T},\overset{\rightharpoonup}{W}} \right)}{{\overset{\rightharpoonup}{W}}^{4}{\overset{\rightharpoonup}{T}}} \times R\;\cos\;\theta_{1}}} & {{Formula}\mspace{14mu} 17} \\\left\lbrack {{Formula}\mspace{14mu} 18} \right\rbrack & \; \\{\int_{- \pi}^{\pi}\ {d\;\phi\left\{ {\frac{\left( {\overset{\rightharpoonup}{T},\overset{\rightharpoonup}{W}} \right)}{{\overset{\rightharpoonup}{W}}^{4}{\overset{\rightharpoonup}{T}}} \times \left( {{R\;\sin\;\theta_{1}\cos\;\phi} - L} \right)} \right\}}} & {{Formula}\mspace{14mu} 18} \\\left\lbrack {{Formula}\mspace{14mu} 19} \right\rbrack & \; \\{{\int_{- \pi}^{\pi}\ {d\;\phi\left\{ {\frac{\left( {\overset{\rightharpoonup}{T},\overset{\rightharpoonup}{W}} \right)}{{\overset{\rightharpoonup}{W}}^{4}{\overset{\rightharpoonup}{T}}} \times \left( {{- R}\;\sin\;\theta_{1}\sin\;\phi} \right)} \right\}}} = 0} & {{Formula}\mspace{14mu} 19}\end{matrix}$

As mentioned above, regarding the component in the rotation direction (ϕdirection), integration of an odd function associated with ϕ isperformed, and hence a result of zero is obtained.

To obtain those numerical values, numerical or analytical integration isperformed. As a result, the deposition state can be simulated. FIG. 10shows components perpendicular to (the deposition surface of) thephotoelectric conversion substrate 21 and obtained by exact solutionusing the above-mentioned cosine rule.

FIG. 10 is a graph showing changes in the length of the perpendicularcomponent of the crystal growth vector relative to the length (=movingradius) L from the center of (the deposition surface of) thephotoelectric conversion substrate 21, assumed when the incident angleθ₁ is set to 45°, 50°, 55°, 60°, 65°, 70° and 75°. In FIG. 10, actualvalues are supposed for Regarding the length L, a range of 0 to 0.5 mwas set as an estimation target. If the photoelectric conversionsubstrate 21 has one side of 17 inches, the maximum value of the lengthL is 0.3 m (=0.43÷2×√{square root over (2)}), where L satisfies thecondition L≤0.5 m).

As is evident from FIG. 10, the perpendicular component of the crystalgrowth vector exhibits good uniformity regardless of the length L.Namely, it is understood that when 45°≤θ₁≤70°, the perpendicularcomponent of the crystal growth vector exhibits good uniformity. Inother words, a uniform deposition thickness can be secured (a uniformthickness can be secured for the fluorescent film 22). It is alsounderstood that when the incident angle θ₁ is varied, the perpendicularcomponent of the crystal growth vector (i.e., the deposited filmthickness) entirely shifts. It is further understood that when theincident angle θ₁ becomes greater, the deposition efficiency is lowered.

FIG. 11 shows the moving radius component. FIG. 11 is a graph showingchanges in the length of the component (along the moving radius) of thecrystal growth vector relative to the length (=moving radius) L from thecenter of (the deposition surface of) the photoelectric conversionsubstrate 21, assumed when the incident angle θ₁ is set to 45°, 50°,55°, 60°, 65°, 70° and 75°. In FIG. 11, L_(O)=1 m and R=1.5 m. Regardingthe length L, a range of 0 to 0.5 m was set as an estimation target.

Regarding the vertical axis of FIG. 11, “−” indicates the inwarddirection of the photoelectric conversion substrate 21, and “+”indicates the outer direction of the photoelectric conversion substrate21. In the inner portions indicated by “−,” the columnar crystalinclines inwardly, while in the outer portions indicated by “+,” thecolumnar crystal inclines outwardly.

As is evident from FIG. 11, in the central position (=rotation axisposition) of (the deposition surface of) the photoelectric conversionsubstrate 21, the averaging effect of the moving radius component of thecrystal growth vector can be obtained by the rotation of thephotoelectric conversion substrate 21, whereby the moving radiuscomponent becomes zero. In contrast, there is a tendency for the movingradius component of the crystal growth vector to increase as the lengthL increases (L>0). This means that the tendency significantly dependsupon the incident angle θ₁. As shown, the inclination of the columnarcrystal is substantially zero where 55°≤θ₁≤60°. The ratio between themoving radius component and the perpendicular component of the crystalgrowth vector falls within ±3%, if L≤0.3 m. Even Where 50°≤θ₁≤65°, theratio between the moving radius component and the perpendicularcomponent falls within ±10%, if L≤0.3 m. Thus, acquisition of crystalwith a practically very excellent perpendicular property can beexpected.

As described above, FIGS. 10 and 11 show the estimation results obtainedwhen L_(O)=1 m and R=1.5 m. FIGS. 12 and 13 show the estimation resultsobtained when L_(O)=1 m and R=1 m.

FIG. 12 is a graph showing changes in the length of the perpendicularcomponent of the crystal growth vector relative to the length (=movingradius) L from the center of (the deposition surface of) thephotoelectric conversion substrate 21, assumed when the incident angleθ₁ is set to 45°, 50°, 55°, 60°, 65°, 70° and 75°. FIG. 13 is a graphshowing changes in the length of the moving radius component of thecrystal growth vector relative to the length (=moving radius) L from thecenter of (the deposition surface of) the photoelectric conversionsubstrate 21, assumed when the incident angle θ₁ is set to 45°, 50°,55°, 60°, 65°, 70° and 75°. Regarding the length L in FIGS. 12 and 13, arange of 0 to 0.5 m was set as an estimation target.

FIGS. 12 and 13 show tendencies similar to those of FIGS. 10 and 11(R=1.5 m). However, it can be understood from these figures that as aresult of the reduction of the distance R, the degree of uniformity ofthe perpendicular components of the crystal growth vectors is reduced,and the degree of variation in the inclinations of the moving radiuscomponents of the crystal growth vectors is increased.

However, even in these cases, the same conclusion as in the cases ofFIGS. 10 and 11 is obtained. Namely, the inclination of the columnarcrystal is substantially zero where 55°≤θ₁≤60°. The ratio between themoving radius component and the perpendicular component of the crystalgrowth vector falls within ±6.5%, if L≤0.3 m. By arranging thephotoelectric conversion substrate 21 to set 55°≤θ₁≤60°, and setting theincident angle θ within a predetermined range, further enhancement ofcrystal perpendicular property can be expected.

Further, even where 50°≤θ₁≤65°, the ratio between the moving radiuscomponent and the perpendicular component falls within a range of −13%to +10%, if L≤0.3 m. Thus, acquisition of crystal with an excellentperpendicular property can be expected. Therefore, when crystal of ascintillator material having a better perpendicular property is needed,it is desirable to set 50°≤θ₁≤65°.

The temperature of the photoelectric conversion substrate 21 during thedeposition period will be described.

In normal deposition, a method of heating a substrate, on which a filmis deposited, to increase the adhesive force of the deposited film isemployed. In this method, enhancement of the adhesive force of the filmis intended by enhancing an active state between the surface of thesubstrate and the evaporated element particles deposited thereon.

The photoelectric conversion substrate 21 is formed by incorporatinga-Si based TFTs 26 and PDs 27 on a glass substrate. Further, aprotective layer is formed as the upper layer of the photoelectricconversion substrate 21, although it is not described above. Theprotective layer is used to smooth the surface of the photoelectricconversion substrate 21, to protect the substrate and to secure theelectrical isolation of the same. In view of the required functions, theprotective layer is an organic film, or a laminated layer of an organicfilm and a thin inorganic film.

When the scintillator material is deposited on the surface of thephotoelectric conversion substrate 21, if the temperature of thephotoelectric conversion substrate 21 is increased, the photoelectricconversion substrate 21 may be damaged or the fluorescent film 22 may bereduced in its adhesive force, thereby degrading the reliability. Itshould be noted that the X-ray image tubes employ a method and astructure in which a scintillator material is deposited on a substrateformed of aluminum, and therefore that it is not necessary to considerthe temperature of the substrate during deposition.

From the above, it is desirable in consideration of the TFT 26, the PD27 and the wiring connections that the temperature of the photoelectricconversion substrate 21 be set less than two hundreds and several tenscentigrades (° C.). Furthermore, in consideration of the organic film(protective film), it is desirable to further reduce the temperature ofthe photoelectric conversion substrate 21.

As the material of the organic film, an acrylic- or silicone-basedorganic resin is particularly often used in view of its opticalproperties, photo-etching pattern forming function, etc. An epoxy resinmay be also used as the material of the protective film. However, thesematerials all have glass transition points, and exhibit increases inthermal expansion coefficient or softening at temperatures above theglass transition points.

Therefore, if the temperature of the protection film (photoelectricconversion substrate 21) significantly exceeds the glass transitionpoint during deposition, the resultant deposited film becomes unstable.In particular, in the initial deposition stage in which the fluorescentfilm 22 starts to be formed on the photoelectric conversion substrate21, the temperature significantly influences the stability of thedeposited film. In contrast, in consideration of the forming of thefluorescent film 22 (crystal film), it is desirable that thephotoelectric conversion substrate 21 be increased to a highertemperature during deposition.

The inventors of the present application tested changes in the state ofthe fluorescent film 22 occurring in association with changes in thetemperature of the photoelectric conversion substrate 21 duringdeposition. More specifically, it was tested whether exfoliation hasoccurred in the formed fluorescent film 22 to thereby determine thequality of the film 22. The temperature of the photoelectric conversionsubstrate 21 was changed during deposition between the initial stage andthe stage thereafter. The initial deposition stage means the timing whenthe fluorescent film 22 starts to be formed on the photoelectricconversion substrate 21. More specifically, the deposition initiatingtiming can be set by opening a shutter provided at the tip (evaporationport) of the crucible 32. The following

TABLE 1 Temperature of photoelectric Temperature of conversion substratephotoelectric in initial stage conversion substrate of deposition afterinitial stage [° C.] [° C.] Result Judgment 100 125 No exfoliation onfluorescent film Excellent No exfoliation on fluorescent film even afterforcing test 125 160-170 No exfoliation on fluorescent film Excellent Noexfoliation on fluorescent film even after forcing test 140 170-190 Noexfoliation on fluorescent film Good Partial exfoliation found afterforcing test 150-180 180-195 Exfoliation found on fluorescent film Bad

As shown in Table 1, where the temperature of the photoelectricconversion substrate 21 was adjusted to 100° C. in the initialdeposition stage, and to 125° C. after the initial stage, no exfoliationoccurred on the formed fluorescent film 22. In this case, even after aforcing test was executed, no exfoliation occurred on the fluorescentfilm 22. The forcing test is, for example, a test in which apredetermined amount of a curable contractible resin, such as an epoxyresin, is coated on the fluorescent film 22 to thereby forcedly loadfilm stress due to curing and contraction on a part of the fluorescentfilm 22.

Where the temperature of the photoelectric conversion substrate 21 wasadjusted to 125° C. in the initial deposition stage, and to 160° C. to170° C. after the initial stage, no exfoliation occurred on the formedfluorescent film 22, and even after the forcing test, no exfoliationoccurred on the fluorescent film 22.

Where the temperature of the photoelectric conversion substrate 21 wasadjusted to 140° C. in the initial deposition stage, and to 170° C. to190° C. after the initial stage, no exfoliation occurred on the formedfluorescent film 22. However, after the forcing test, exfoliationoccurred on the fluorescent film 22.

Where the temperature of the photoelectric conversion substrate 21 wasadjusted to 150° C. to 180° C. in the initial deposition stage, and to180° C. to 195° C. after the initial stage, exfoliation occurred on theformed fluorescent film 22.

The temperature of the photoelectric conversion substrate 21 in theinitial deposition stage especially influences the stability of adhesionof the fluorescent film 22 to the photoelectric conversion substrate 21.If the temperature of the photoelectric conversion substrate 21 in theinitial deposition stage exceeds 140° C., the risk of exfoliation of theformed fluorescent film 22 may significantly increase. Therefore, it isdesirable to limit the temperature of the photoelectric conversionsubstrate 21 to 140° C. or less in the initial deposition stage.

After the initial deposition stage, an appropriate fluorescent film 22with no exfoliation could be formed even at 125° C., as is mentionedabove. Although film forming is possible even at a temperature less than125° C., a temperature of 125° C. or more is appropriate, because thetemperature after the initial deposition stage is associated with thecrystal growth condition for the fluorescent film 22 and may alsoinfluence the properties of the fluorescent film 22, such assensitivity. Therefore, 125° C. or more is appropriate range.

This being so, after the initial deposition stage, it is desirable toset the temperature of the photoelectric conversion substrate 21 withina range of 125° C. to 190° C. In this case, the fluorescent film 22 canbe formed without exfoliation. As described above, in view of theadhesion stability of the fluorescent film 22 on the photoelectricconversion substrate 21, an upper limit for the temperature of thephotoelectric conversion substrate 21 during deposition is determined.

On the other hand, a lower limit for the temperature of thephotoelectric conversion substrate 21 during deposition is determined inview of characteristics. The inventors found that the sensitivitycharacteristic of the X-ray detection panel 2 correlates with thetemperature of the photoelectric conversion substrate 21 in the initialdeposition stage.

If the temperature of the photoelectric conversion substrate 21 in theinitial deposition stage falls within a range of 65° C. to 85° C., thesensitivity characteristic is averagely proportional by a ratio of about0.6 to the temperature of the photoelectric conversion substrate 21 inthe initial deposition stage, although it is influenced by variousfactors. Accordingly, if the temperature of the photoelectric conversionsubstrate 21 in the initial deposition stage decreases, the sensitivitycharacteristic of the X-ray detection panel 2 decreases.

Further, if the temperature of the photoelectric conversion substrate 21in the initial deposition stage decreases, the temperature of thephotoelectric conversion substrate 21 after the initial deposition stagemay well decrease. As a result, the above-mentioned influence on thecrystal growth may occur. Furthermore, the above-described sensitivityreduction phenomenon could be confirmed. In view of the risk ofreduction in the sensitivity of the X-ray detection panel 2, it isdesirable to set, to 70° C. or more, the temperature of thephotoelectric conversion substrate 21 in the initial deposition stage.

Moreover, from the above-described test results, when the scintillatormaterial is deposited on the photoelectric conversion substrate 21, itis preferable in the embodiment to control the temperature of thephotoelectric conversion substrate 21 in the initial deposition stage tothe range of 70° C. to 140° C., and to control the temperature of thephotoelectric conversion substrate 21 after the initial deposition stageto the range of 125° C. to 190° C.

It is further preferable to control the temperature of the photoelectricconversion substrate 21 in the initial deposition stage to the range of70° C. to 125° C., and to control the temperature of the photoelectricconversion substrate 21 after the initial deposition stage to the rangeof 125° C. to 170° C.

A description will then be given of thermal conduction occurring insidethe vacuum chamber 31.

FIG. 14 shows the photoelectric conversion substrate 21, the heatconductor 36, the holding mechanism 37 and the radiator 38 shown in FIG.3, and is useful for explaining the function of the heat conductor 36.As aforementioned, to form the fluorescent film 22, a furnace of a largesize is used as the crucible 32, and a scintillator material of severalkilograms (e.g., 6 kg) is input into the crucible 32. The crucible 32 isheated to about 700° C. higher than the melting temperature of CsI.

Accordingly, a great amount of radiation heat is generated by thecrucible 32, and the photoelectric conversion substrates 21 located atupper positions in the vacuum chamber 31 are heated intensely, as isshown in FIGS. 3 and 8. Further, since the evaporated element particlesimpart thermal energy to the photoelectric conversion substrates 21during deposition, the temperature of the photoelectric conversionsubstrates 21 is greatly increased.

In light of this, the heat conductors 36 are opposed to thephotoelectric conversion substrates 21 and the holding mechanisms 37such that the former components cover the entire surfaces of the lattercomponents. Assume here that the surface of each heat conductor 36opposing the corresponding photoelectric conversion substrate 21 andholding mechanism 37 is defined as an obverse surface S1, and the othersurface of each heat conductor 36 opposing the corresponding radiator 38is defined as a reverse surface S2. Since the obverse surfaces S1 of theheat conductors 36 can absorb the heat emitted from the photoelectricconversion substrates 21 and the holding mechanisms 37, thephotoelectric conversion substrates 21 can be protected fromoverheating, whereby the temperature of the substrates 21 can becontrolled to the above-mentioned appropriate value.

Further, the heat conductors 36 can transmit radioactive heat to theradiators 38 from the reverse surface 2 side. When the heater of theradiators 38 are not driven, the radiators 38 function to transmit heatto the walls of the vacuum chamber 31 through heat conduction.

Radiation heat can be more efficiently transmitted between opposingmembers when the distance between the members is shorter. Accordingly,in the embodiment, each heat conductor 36 is interposed between holdingmechanism 37 (photoelectric conversion substrate 21) and radiator 38 tomake, as short as possible, the distance between the heat conductor 36and the holding mechanism 37 (photoelectric conversion substrate 21),and the distance between the heat conductor 36 and the radiator 38.

Further, it is desirable to make the emissivities of the obverse andreverse surfaces S1 and S2 close to 1 to thereby form the heatconductors 36 of a material having a high heat conductivity. In thiscase, overheating of the photoelectric conversion substrates 21 can befurther suppressed.

In the embodiment, the obverse and reverse surfaces S1 and S2 of theheat conductors 36 are subjected to a blackening treatment, whereby theheat conductors 36 can secure high emissivity. The blackened surfaces S1and S2 exhibit an emissivity of about 95%, while a metal (e.g.,aluminum) glazing surface exhibits an emissivity of several tenspercents. Thus, it can be understood that the obverse and reversesurfaces S1 and S2 perform complete black-body radiation. It is moreeffective if the surfaces of the holding mechanisms 37 and the radiator38 are also subjected to the blackening treatment for enhancing theiremissivities.

In the method of manufacturing the X-ray detection panel descriptionabove, when a radiation panel is produced, the photoelectric conversionsubstrates 21 are arranged so that 45°≤θ≤70° is satisfied at the centerof each photoelectric conversion substrate 21. After that, thefluorescent films 22 are formed by depositing the scintillator materialon the photoelectric conversion substrates 21.

By setting θ not less than 45° (45°≤θ) at the center of eachphotoelectric conversion substrate 21, the load on, for example, thevacuum exhaust device can be reduced to thereby enhance the productivityand the efficient of use of the scintillator material. In particular, inthe manufacture of large X-ray detection panels 2, the productivity canbe enhanced. In addition, by setting θ not more than 70° (θ≤70°) at thecenter of each photoelectric conversion substrate 21, (Dh/Dv)<1 can beestablished, thereby enabling a finer columnar crystal to be formed.This contributes to enhancement of the resolution of the X-ray detectionpanel 2.

The embodiment utilizes vacuum vapor deposition performed under apressure of 1×10⁻² Pa or less. As a result, columnar crystal thickeningcan be suppressed, and crystal growth along the normal lines of thephotoelectric conversion substrates 21 be accelerated.

Further, in the embodiment, the rotational speed of the photoelectricconversion substrates 21 is set to 4 rpm or more. As a result, the MTFvalues are gradually increased, which contributes to enhancement of theresolution of the X-ray detection panel 2.

When depositing the scintillator material on the photoelectricconversion substrates 21, the temperature of the photoelectricconversion substrates 21 is controlled within a range of 70° C. to 140°C. in the initial deposition stage, and the temperature of thephotoelectric conversion substrates 21 is controlled within a range of125° C. to 190° C. after the initial deposition stage. As a result, thefluorescent films 22 can be formed without exfoliation, whichcontributes to forming of an X-ray detection panel 2 with excellentsensitivity.

As described above, the embodiment can provide the method ofmanufacturing the X-ray detection panel 2 capable of enhancingproductivity, and capable of forming a fluorescent film 22 thatcontributes to enhancement of the resolution characteristic of the X-raydetection panel 2. The embodiment can also provide the method ofmanufacturing the X-ray detection panel 2 capable of forming fluorescentfilms 22 with a high manufacturing yield.

Although a certain embodiment has been described above, it is merely anexample and does not limit the scope of the invention. Variousomissions, various replacements and/or various changes may be made inthe embodiment without departing from the scope of the invention. Theembodiment and their modifications are included in the scope of theinvention, namely, in the inventions recited in the claims andequivalents thereof.

For instance, in the above-described embodiment, two X-ray detectionpanels 2 are simultaneously manufactured. However, the above-describedadvantage can be obtained even when only one X-ray detection panel 2 ismanufactured, or when three X-ray detection panels 2 are simultaneouslymanufactured. When simultaneously manufacturing three X-ray detectionpanels 2, the vacuum deposition device 30 comprises three heatconductors 36, three holding mechanisms 37, three radiators 38 and threemotors 39. For example, the three holding mechanisms 37 can be arrangedat circumferential intervals of 120° around the axis (vertical axis) ofthe crucible 32.

Only CsI may be input into the crucible 32. In this case, theabove-mentioned advantage can also be obtained if TlI is input intoanother crucible (a small crucible) prepared in addition to the crucible32 (a large crucible), thereby simultaneously depositing CsI and TlI.

The shape of the heat conductors 36 is not limited to a plate-like one,but may be changed in various ways such a block structure. It issufficient if the heat conductors 36 have a shape that matches thearrangement of the photoelectric conversion substrates 21, the shape ofthe holding mechanisms 37, the positions of the radiators 38, etc.Although in the above-described embodiment, the heat conductors 36 areformed of aluminum to enhance the thermal conductivity, the material ofthe conductors is not limited to aluminum. The heat conductors 36 may beformed of, for example, copper (Cu).

Although in the above embodiment, the scintillator material containscesium iodide (CsI) as a main component, it is not limited to this. Evenif another material is used as the scintillator material, a similaradvantage to the above can be obtained.

The above-described technique is not limited to an apparatus and methodof manufacturing X-ray detection panels, but is also applicable to anapparatus and method of manufacturing various types of radiationdetection panels.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A method of manufacturing a radiation detectionpanel, comprising: positioning a photoelectric conversion substratevertically above an evaporation source such that a deposition surface ofthe photoelectric conversion substrate is exposed to the evaporationsource and inclined with respect to a vertical axis; and evaporating ascintillator material and emitting the scintillator material verticallyupward by the evaporation source to deposit a fluorescent film on thedeposition surface, wherein when the scintillator material is depositedon the deposition surface, the photoelectric conversion substrate isrotated, the photoelectric conversion substrate is positioned to satisfy45′≤θ≤70° at a center of the deposition surface, where θ is an anglemade inside between an incident direction of the scintillator materialand a normal line of the deposition surface; and the photoelectricconversion substrate is rotated by setting a rotation axis as an axisalong a normal line of the center of the deposition surface.
 2. Themethod of claim 1, wherein the photoelectric conversion substrate ispositioned to satisfy 50°≤θ≤65° at the center of the deposition surface.3. The method of claim 1, wherein an angle between a vertical axispassing through the scintillator material and the deposition surface isless than 30°.
 4. The method of claim 1, wherein a vacuum depositionmethod in which deposition is performed under a vacuum pressure of1×10⁻² Pa or less is utilized.
 5. The method of claim 1, wherein thephotoelectric conversion substrate is rotated at a rotational speed of 4rpm or more.
 6. The method of claim 1, wherein the scintillator materialcontains cesium iodide (CsI) as a main component.